In the prior art, processes permitted forming on the same substrate unipolar and bipolar transistors intended to complement each other in whatever circuit function they performed while retaining their independent characteristics. It also has been possible by other process techniques to fabricate functioning bipolar transistors on SOS. The process, however, was very complex and was not compatible with the fabrication of CMOS devices on the same chip. The bipolar transistors also were not lateral and did not take advantage of the poly-silicon mask as in the present invention.
The present invention provides a process for the simultaneous fabrication of CMOS transistors and bipolar devices on the same integrated circuit. The key point is the use of polysilicon as a diffusion mask edge for both the emitter and base. This permits the fabrication of lateral bipolar devices having narrow base widths (i.e., W.sub.B &lt; 5000A) since the base width is determined only by the base and emitter diffusion parameters i.e., concentration time, and temperature) and not by any lateral dimension.